Chapter 10 Chemical Bonding II: Molecular Shape, Valence Bond Theory, and Molecular Orbital Theory 10.1 Artificial Sweetness: Fooled by Molecular Shape - Taste of food depends on interaction between food molecules and taste cells on tongue main factors affecting the interactions are shape of molecule and change distribution within molecule Food molecule will fit into active site of specialized proteins and when this happens, changes in the protein structure= nerve signal to transmit - Sugar molecules fit into active site of taste cell receptors called T1r3 protein receptor proteins sugar molecule (key) entering active site (lock) = different subunits of T1r3 protein split apart ion channels open and nerve signal transmitted artificial sweeteners fit into the T1r3 receptor making it stronger than sugar (sweeter) - Properties of molecules depend on structure of molecule (factors include skeletal arrangement of atoms, kind of bonding and shape of molecule) - Molecule are 3-D objects (describe shape of molecule with terms that relate to geometric figures, which have characteristics corners that indicate position of surrounding atoms around central atoms, and bond angles) - Lewis Theory predicts electron groups (regions of electron in an atom, some are paired while other are unshared) these regions should repel one another (negative charge) to predict shape of molecules (position is determined by where the bonding electron groups are and will be determined by trying to minimize repulsion between then) - VSEPR Theory: Valence Shell Electron Pair Repulsion Theory because electrons are negatively charged, they should be most stable when they are separated as far as possible 10.2 VSEPR Theory: The Five Basic Shapes - 5 basic arrangements of electron groups around a central atom (maximum 6 bonding electron groups, though there maybe > 6 on very large atoms but is RARE) - 5 basic arrangements result in 5 different basic geometries (in order for molecule shape and bond angles to be perfect geometric figure, all electron groups must be bonds and all bonds are equivalent, resonance does not matter) 1) Linear: 2 electron groups = occupy positions on opposite sides, bond angle = 180 www.notesolution.com